Category Archives: Materials

Metamaterials are a class of material engineered to produce properties that don’t occur naturally.

The first working demonstration of an “invisibility cloak” was achieved in 2006 at the Duke University Pratt School of Engineering using the complex metamaterial-based cloak shown below.

Source: screenshot from YouTube link below.

The cloak deflected an incoming microwave beam around an object and reconstituted the wave fronts on the downstream side of the cloak with little distortion. To a downstream observer, the object inside the cloak would be hidden.

Source: screenshot from YouTube link below.

You can view a video of this Duke invisibility cloak at the following link:

In a paper published in the 18 September 2015 issue of Science, researchers at UC Berkley reported creating an ultra-thin, metamaterial-based optical cloak that was successful in concealing a small scale, three-dimensional object. The abstract of this paper, “An ultrathin invisibility skin cloak for visible light”, by Ni et al., is reproduced below.

“Metamaterial-based optical cloaks have thus far used volumetric distribution of the material properties to gradually bend light and thereby obscure the cloaked region. Hence, they are bulky and hard to scale up and, more critically, typical carpet cloaks introduce unnecessary phase shifts in the reflected light, making the cloaks detectable. Here, we demonstrate experimentally an ultrathin invisibility skin cloak wrapped over an object. This skin cloak conceals a three-dimensional arbitrarily shaped object by complete restoration of the phase of the reflected light at 730-nanometer wavelength. The skin cloak comprises a metasurface with distributed phase shifts rerouting light and rendering the object invisible. In contrast to bulky cloaks with volumetric index variation, our device is only 80 nanometer (about one-ninth of the wavelength) thick and potentially scalable for hiding macroscopic objects.”

If you have a subscription to Science, you can read the full paper at the following link:

Eric Grundhauser writes on the Atlas Obscura website about an interesting quandary for users of an optical invisibility cloak.

“Since your vision is based on the light rays that enter your eyes, if all of these rays were diverted around someone under an invisibility cloak, the effect would be like being covered in a thick blanket. Total darkness.”

So, the Invisible Man is likely to be less of a threat than he appeared in the movies. You should be able to locate him as he stumbles around a room, bumping into everything he can’t see at visible light frequencies. However, he may be able to navigate and sense his adversary at other electromagnetic and/or audio frequencies that are less affected by his particular invisibility cloak.

You can read Eric Grundhauser’s complete article, “The Problem With Invisibility is Blindness,” at the following link:

Recognizing this inconvenient aspect of an invisibility cloak, researchers from Yunnan University, China, have been investigating the concept of a “reciprocal cloak,” which they describe as, “an intriguing metamaterial device, in which a hidden antenna or a sensor can receive electromagnetic radiation from the outside but its presence will not be detected.” One approach is called an “open cloak,” which includes a means to, “open a window on the surface of a cloak, so that exchanging information and matter with the outside can be achieved.”

You can read the complete 2011 paper, “Electromagnetic Reciprocal Cloak with Only Axial Material Parameter Spatially Variant,” by Yang et al., at the following link:

An all-aspect, broadband (wide range of operational frequencies) invisibility cloak is likely to remain in the realm of fantasy and science fiction. A 10 March 2016 article entitled, “Invisibility cloaks can never hide objects from all observers,” by Lisa Zyga, explains:

“….limitations imposed by special relativity mean that the best invisibility cloaks would only be able to render objects partially transparent because they would suffer from obvious visible distortions due to motion. The result would be less Harry Potter and more like the translucent creatures in the 1987 movie Predator.”

Further complications are encountered when applying an invisibility cloak to a very high-speed vessel. A 28 January 2016 article, also by Lisa Zyga, explains:

“When the cloak is moving at high speeds with respect to an observer, relativistic effects shift the frequency of the light arriving at the cloak so that the light is no longer at the operational frequency. In addition, the light emerging from the cloak undergoes a change in direction that produces a further frequency shift, causing further image distortions for a stationary observer watching the cloak zoom by.”

You can read the complete article, “Fast-moving invisibility cloaks become visible,” at the following link:

In a 31 December 2015 post, I discussed the “U.S. Commercial Space Launch Competitiveness Act,” which was signed into law on 25 November 2015 and established, among other things, the legal basis for asteroid mining. I also identified the firm Planetary Resources (http://www.planetaryresources.com/ – home-intro) as one of the firms having a business interest in asteroid prospecting.

Today, at the Consumer Electronics Show (CES) today in Las Vegas, Planetary Resources announced that they, in collaboration with their partner firm, 3D Systems (http://www.3dsystems.com), have produced the first ever direct metal print of an object using metals recovered from an asteroid (or meteorite) that impacted Earth.

Source: Planetary Resources

In the Planetary Resources announcement, they stated that the material used for 3D printing:

“…was sourced from the Campo Del Cielo impact near Argentina, and is composed of iron, nickel and cobalt – similar materials to refinery grade steel.”

The milestone announced today demonstrates a key capability needed for building research bases and commercial facilities in space using raw materials found on another body in our solar system.

Imagine what the cargo manifest will be on future space missions to destinations that have useful natural resources that can be mined and prepared on site for use in various 3D printing (additive manufacturing) activities. The early missions will need to carry pre-fabricated structures for an initial base, tools for initial mining and manufacturing work, other items manufactured on Earth, and consumables. Once the on-site mining and manufacturing facilities reach an initial operating capability, the extended supply chain from Earth can be reduced commensurate with the capabilities of the local supply chain.

For more background information on this subject, National Academies Press published the report, “3D Printing in Space”, which you can download for free at the following link if you have set up a MyNAP account:

Opportunities for 3D printing in space addressed in this NAP report include: manufacturing new or replacement parts needed on a space vehicle or off-Earth facility; creating structures that are difficult to produce on, or transport from, Earth; creating a fully-printed spacecraft; using resources available on planetary surfaces; recycling materials in space; and establishing a free-flying fabrication facility. The report also includes roadmaps for NASA and the U.S. Air Force deployment of 3D printing capabilities in space.

This is just the start. Manufacturing in space using locally sourced materials will revolutionize our approach for building a permanent human presence off the planet Earth.

Graphene is a 2-dimensional (one atom thick) structure of graphite, composed of carbon atoms tightly bonded together in a hexagonal lattice. These physical properties give graphene an extraordinary combination of high strength, low weight, high thermal and electrical conductivity.

Source: Gizmag.com

The firm Graphena is a commercial graphene supplier. Their website is a good source of information regarding graphene technology. Basic graphene properties are explained at the following link:

Photovoltaic cells: cost-effective, high-efficiency replacement for silicon solar cells in current applications, and new applications for flexible PV cells such as window screens and installations on curved surfaces.

Energy storage: higher-capacity supercapacitors and batteries

A key limitation to developing graphene applications has been the relatively high cost of manufacturing graphene. Presently, chemical vapor deposition (CVD) is the process commonly used to manufacture high-quality graphene on a large scale. A breakthrough in lower-cost CVD manufacturing technology recently was announced by the firm Carbon Sciences, Inc. and the University of California Santa Barbara (UCSB). You can read more about this announcement at the following link: